I need help sizing my water heater or boiler

toddstanley

I have an 1800 square foot slab with 1/2" PEX tubing installed in the slab. I used a radiant barrier product in the slab too. I am now at the point where I need to install/choose to go with a hot water heater or boiler and am looking for a solution. Here's what makes this hard for me. This is not a home! It is a green house therefore when you talk about heating loss, etc. I have no idea how to calculate for this. Also, because the radiant system isn't necessarily to heat the air in the green house per se - the idea is to keep the slab itself at around 67-68 and the air temp no more than 72. I've read and read about boilers, hot water heaters, closed loop vs open, etc. There isn't anywhere I've been able to find out how to size my boiler/hot water heater. I'm leaning on the hot water heater as it seems a bit more economical in an open loop system so I can also use the hot water which will be run through a high pressure washer system that can handle water up to 120 degrees. I've also built and installed an open loop system using a polaris hot water heater in my home and have a bit of an understanding of how to plumb it together etc. I just feel like a polaris would be way overkill for my situation??? I've also looked at some of the wall mounted on demand tanks but those seem like they may be undersized? I don't know because I can't figure out how many BTU's, etc in the first place which is why I was happy to find this site. Does anyone have any ideas or suggestions for me? Thank you very much in advance for your input. Also you should know the location of this is Sacramento California to help with the whole BTU thing.

toddstanley

another reason why it feels like the heater doesn't need to be sized very large is because you have the sun helping to keep the green house warm, which is the idea behind a green house in the first place.

Jamie Hall

Actually not rocket science -- in fact, the heat loss can be figured like any other building. Except, of course, there is a lot of window and not much wall!

The real trick is finding the heat loss of the greenhouse glazing you plan to use, since that varies all over the place (plastic? glass? single? double? air gap?). Fortunately, that information should be available from the manufacturer, if it's a purpose built product, or figured in exactly the same way as a window would be.

There are greenhouse heat loss calculations -- Google "greenhouse heating calculator" -- which will do the job nicely, so long as you remember that most of them are proprietary to the various greenhouse materials manufacturers.

Once you have the heat loss, then you're really home free. You could come back here (and be very welcome) and I'm sure that you will get a variety of suggestions. I myself am not really keen on open systems, and I'm certainly not keen on using water heaters as heating appliances -- they aren't meant for it. However, you might find that one of the smaller mod-con heating boilers would be a decent fit. You might also find an air to water heat pump with the required capacity; in Sacramento you don't have to worry so much about the problem of such critters losing efficiency when it gets too cold outside.